Deployment of chloride tolerant cultivars is an effective approach to minimize yield loss in a saline soil. In soybean, Glycine max (L.) Merr., substantial genetic variation exists for a response to salt stress. However, breeding for chloride tolerance is hampered because no economically viable screening method has been developed for practical breeding.
Salt stress can lead to symptoms such as stunted growth, reduced yield and death in sensitive soybean species. As agricultural land is increasingly salinized through inefficient fertilizer practices, chloride-water intrusion, and use of poor quality irrigation water, development of chloride tolerant cultivars becomes increasingly important as a means of combating salt-related yield losses.
In soybean, the salinity stress inhibits seed germination and seedling growth, reduces nodulation, and decreases biomass accumulation and seed yield. Previous studies identified the Ncl gene on linkage group N, which confers tolerance to the plant through chloride exclusion; not allowing Cl(−) to translocate from the roots into the rest of the plant where it can accumulate and become toxic. However, the markers available to identify this gene are not predictive and do not translate well from the laboratory to the field. As many as 20% of soybean cultivars released for the southern USA have economic levels of chloride tolerance, but no economically viable screening method for chloride tolerance has been developed for practical breeding use. Marker assisted breeding has been proposed to accelerate the development of chloride tolerant cultivars; however, there are few commercial examples of successful marker-assisted breeding for tolerance to chloride, or other abiotic stresses, in soybean.
For these reasons, chloride tolerance may be a particularly good candidate for adaptation to marker-assisted breeding. A prerequisite for such a breeding effort is knowledge of the genomic location of the major gene for chloride tolerance in soybean.